This invention relates to a fixing structure for fixing an object to a fixing plate by using a couple of screws, particularly, to a fixing structure for fixing an automobile antenna unit for receiving digital radio broadcasting to an outer plate of an automobile by using a couple of screws, and to the automobile antenna unit having the fixing structure.
Digital radio broadcasting in the United States of America uses a high frequency band such as 2 GHz. Accordingly, a receiving antenna unit for the digital radio broadcasting must be placed out of doors. When a digital radio receiver is mounted on an automobile, an automobile antenna unit for the digital radio receiver must be fixed to an outer plate such as a roof of the automobile.
A related automobile antenna unit has a related fixing structure using first and second screws which can be engaged with each other. The first screw is permanently fixed to the antenna unit while the second screw is not fixed to the antenna unit. The first screw is a nut while the second screw is a bolt, for instance.
The outer plate of the automobile provides a fixing hole to fix the antenna unit. The antenna unit is put on an upside of the outer plate to cover the fixing hole. The second screw is combined with the first screw from an underside of the outer plate to attach a fixing attachment. By tightening the second screw against the first screw, the outer plate is held tight between the antenna unit and the fixing attachment. Thus, the antenna unit is fixed to the outer plate of the automobile.
When the second screw is tightened against the first screw, the antenna unit receives rotating force through the first screw. To prevent the antenna unit rotating, the related fixing structure has a locator pin provided on a bottom of the antenna unit. Correspondingly, a locating hole is provided in the outer plate of the automobile. The fixing hole and the locating hole are aligned in a predetermined direction with respect to the automobile to orient the antenna unit in the predetermined direction. Similarly, the locator pin and the first screw are aligned in the predetermined direction on condition that the antenna unit is oriented in the predetermined direction.
To mount the antenna unit on the outer plate of the automobile, clearance between the locating hole and the locator pin is necessary. However, the clearance allows rotation of the antenna unit when the second thread member is tightened. Accordingly, the related fixing structure has a problem of low accuracy regarding to a direction of the antenna unit.